Since the time of Columbus, explorers dreamed of a water passage across the North American continent. President Thomas Jefferson shared this dream. He conceived the Corps of Discovery to travel up the Missouri River to the Rocky Mountains and westward along possible river routes to the Pacific Ocean. Meriwether Lewis and William Clark led this expedition of 1804-6. Along the way they filled hundreds of notebook pages with observations of the geography, Indian tribes, and natural history of the trans-Mississippi West. This volume consists of journals, primarily by Clark, which cover the expedition’s route up the Missouri River to Fort Mandan in present-day North Dakota and its frigid winter encampment there. It describes the party’s encounters and observations of area Indian tribes. Lewis and Clark collected critical information about traveling westward from Native Americans during this winter. This volume also includes miscellaneous material from the Corps of Discovery’s first year. Gary E. Moulton is Thomas C. Sorensen Professor of American History at the University of Nebraska and the recipient of the J. Franklin Jameson Award of the American Historical Association for the editing of these journals.